January 28, 2004
Boston Cure Project
Magnetization transfer imaging is a technique that has in recent years been used to detect axonal damage and demyelination in MS brain lesions. A new study in the journal Brain describes its use in studying changes in optic nerve lesions over time. 21 patients with optic neuritis (plus healthy controls) were imaged multiple times over the course of a year and the optic nerve magnetization transfer ratio (MTR) was assessed. The results showed a slow decline in MTR for the diseased nerves over time, with the MTR bottoming out at an average of eight months and then slightly increasing again. (A reduction in MTR means loss of myelin and axonal damage.)
Some interesting points from this study include: (1) MTR in optic nerve lesions continues to decline even while visual recovery is taking place, implying that restoration of function can occur simultaneously with tissue breakdown. This might be due to the use of redundant capacity elsewhere, the insertion of new sodium channels to restore conduction, or other factors. (2) The slow decline in MTR contrasts with the quick drop in MTR seen in acute brain lesions, so perhaps something about the structure of the optic nerve hinders the removal of the myelin debris, making the process take longer. (3) The slight increase in MTR seen in some subjects at the one-year point might indicate remyelinating activity, although longer-term follow-up is needed to determine whether this increase is significant and long-lasting.
Imaging has its limitations, but it's the only way to monitor changes in the nervous system in MS over time and new, more informative technologies are being developed all the time. Serial imaging studies such as this one are an encouraging development in the effort to understand what really happens in MS.
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